The operation of an internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and nitrous oxide (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of an engine piston forces exhaust gas, which may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.
Reduced internal combustion engine exhaust gas emissions and improved engine performance of an engine may be achieved by adjusting the actuation timing of the engine valves. For example, the actuation timing of the intake and exhaust valves may be modified to implement a variation on the typical diesel cycle or Otto cycle known as the Miller cycle. In a “late intake” type Miller cycle, the intake valves of the engine are held open during a portion of the compression stroke of the piston.
Engines implementing a late intake Miller cycle may include a fluid actuator capable of varying the closing timing of mechanically operated intake valves. In such systems, the fluid actuator may experience impact forces against an actuator chamber wall associated with the closing of the intake valves by the stiff return springs. Consequently, the fluid actuator may suffer erosion, fracture, and/or breakage.
U.S. Pat. No. 5,577,468 discloses an engine having a snubbing assembly for reducing the flow of fluid from the fluid actuator, and thereby reduce the intake valve seating velocity. However, in that engine, the piston of the fluid actuator and the snubbing assembly are implemented separately from one another, thus requiring independent manufacture of multiple components at tight tolerances, complicating assembly and repair/replacement, and occupying valuable space in the engine compartment, all of which may result in increased costs to the manufacturer.
The variable valve actuation system of the present invention solves one or more of the problems set forth above.